Electron multiplier



Sept. 3, 1940. E RUSKA I ELECTRON MULTIPI IER Filed Aug. 19, 1937 7 9 rI I zfi J ,2 3 4 .5 6' '7 c9 3mm MM Patented Sept. 3, 1940 ELECTRONll/IULTEPLEER Ernst Rnslra, Berlin-Zehlendorfi Germany, as-- signor tothe firm Fernseh Ailrtien-Gesellschaft, Zehlen'dori", near Berlin,Germany Application August 19, 1937, Serial No. 159,993 lln GermanySeptember 7, 1938 2 Claims.

This invention relates to'multistage electron multipliers. It is theobject of this invention to produce a multiplier of great simplicity andsmall dimensions.

Multistage electron multipliers are known in which electrons emittedfrom an emitting eleo trode are accelerated by an electrode opposite tothe emitting electrode and travel along arcshaped paths under theinfluence of a magnetic field and impact a second electrode adjacent tothe first emitting electrode. This process, of course, can be repeated.In such an arrangement the magnetic field which creates the desiredelectron paths is Vertical to the plane of the drawing of Fig. 1, whichdiagrammatically shows a series of emitting electrodes, l to 8, and aseries of accelerating electrodes 2' to l. Thereby the electrodes 2, 2'and 3, 3, etc., are held at the same potential. For production of such amag,- netic field either permanent magnets are used, the poles of whichare parallel to the plane of the drawing, or elongated rectangular coilsare provided to both sides of the electron arrangement. The applicationof permanent magnets is undesirable in many cases, especially if thearrangement is to be housed in a vacuum or if the stray fields causeinterferences. Also, the production of rectangular coils isinconvenient. Especially if a multiplier of this kind is to be combinedwith a picture analyzing tube it is desirable to employ simple coilforms which require very little space.

Figs. 1 and 2 are two views illustrating schematically, the principleunderlying the operation of the present invention.

Figs. 3, 4 and 5 are views in section, of various embodiments of theinvention.

This invention is based on the idea that a magnetic field parallel tothe plane of the drawing of Fig. 1 in the direction of the arrow A mayproduce arc-shaped electron paths under certain conditions, viz., if theelectrons emitted from an electrode do not travel in the direction ofthe arrow A because of an accelerating field, but in a transversedirection, i. e., in the direction of the arrow B. Thus, considering thetransverse component of the electron velocity one will see that amagnetic field in the direction of the arrow A will produce a deflectionwhich results in an arc-shaped path of the electrons perpendicular tothe plane of the drawing. Fig. 2 shows a view from the top of thearrangement shown in Fig. 1. In this figure the electrons would travelin the direction of the arrow C, so that electrons starting at the point9 would imthe lowest potential.

pact in a point ill. However, the electrostatic field also causes avelocity component in the direction of the arrow A, so that theresulting electron path it is obtained which reaches from the lower leftcorner of the arrangement in Fig. 2 to the upper right corner and whichconsists of individual arc-shaped sections.

The electrode arrangement must expand sufficiently in the direction ofthe arrow 0 so that that the electrons will still be able to impact thelast electrode. In order to achieve a compact construction, it is anobject of the invention to use ring-shaped electrodes, whereby thisdifiiculty is eliminated. The electrons travel in heliXes around thering-shaped electrodes, the diameter of which can be made very smallbecause it is possible to allow the electrons to make one or severalcomplete rotations around the ringshaped arrangement.

Several embodiments of the invention are shown in the Figs. 3, 4 and 5.In Fig. 3 the electrodes E2 to iii are ring-shaped. The electrodes aredisposed in the interior of a cylindrical tube it, which is surroundedby a coaxial cylindrical coil E9. The electrodes are held at increasingpotentials whereby the electrode l2, which may be a photocathode, isheld at the lowest and the anode ll at the highest potential. Thelongitudinal magnetic field influences the electrons of primarilytransverse velocity in such a manner that they travel in a helix-shapedpath 2% from one electrode to the other. In order to make uniform use ofthe ring-shaped electrodes it is advisable to produce an emission fromthe entire outer area of the primary electrode ii. In this manner asymmetrical arrangement is obtained which may be placed in a long narrowtube. Such an arrangement is especially preferable if the amplifierreceives its primary electrons through the scanning aperture of apicture-analyzing tube. The voltage drop along the coil it can besimultaneously employed to produce the electrostatic accelerating field.The coil in this case, is not layer wound, but wound from one end to theother so that the windings next to the anode l'l possess the highestpotential, and the windings next to the first electrode l2 possess Thecoil can be arranged inside or outside of the vacuum. If it is notpossible to produce the required magnetic field and electrostatic fieldby means of the same coil, it is advisable to provide specialaccelerating electrodes 2i to 27, which also are ring-shaped and whichconcentrically surround the emitting electrodes E2 to H, as isillustrated in Fig. 4. Each emitting electrode is connected with theaccelerating electrode of the previous stage. In this case the primaryelectrons are produced by a thermionic cathode 36.

As Fig. 5 shows, this arrangement may also be reversed, i. e., theemitting electrodes l2 to ll are placed outside and the acceleratingelectrodes 28 to 32 are placed inside. In such an arrangement ahelix-shaped path of electrons is also obtained, which path consists ofindividual arcshaped sections. In the embodiment shown in Fig. 5 themagnetic coil 34 is placed in the interior of the vacuum receptacle. Inorder to save leads, the voltage drop along the coil is given such avalue that the potentials for the electrodes may be taken from the coil.By doing so only three sealed-in leads are necessary for any number ofelectrodes. The first accelerating electrode, from which no liberationof electrons takes place, is a cone-shaped mirror 33 coaxial to the tubeinside of the ring I2. A coaxial ray of light is directed upon thismirror by means of the lens 31 so that the electrode i2 is uniformlyilluminated.

I claim:

1. An electron multiplier comprising an electrode assembly involving aplurality of electrodes having electron emissive properties, a series ofaccelerating anodes each disposed in proximity to an electron emissiveelectrode, leads conncted to said assembly for enabling establishment ofpotentials of increasing values on successive anodes in said series, aconnection from each of said anodes to the electron emissive electrodeassociated with the anode of next higher potential in the series toenable setting up a potential gradient between successive electronemissive electrodes, and means for providing a magnetic field in thedirection of said potential gradient.

2. An electron multiplier comprising an electrode assembly involving aplurality of electrodes having electron-emissive properties, one of saidelectron-emissive electrodes being photosensitive; lead connections tosaid electrode assembly for enabling a potential gradient to beestablished between successive electrodes; means for provid ing amagnetic field in the direction of said potential gradient; anaccelerating anode disposed in proximity to each of saidelectron-emissive electrodes; and light-reflecting means symmetricallylocated with respect to said photosensitive electrode for providing asubstantially uniform distribution of reflected light over the surfaceof said photosensitive electrode.

ERNST RUSKA.

